In recent years the demand for disposable absorbent articles, such as disposable diapers has been increasing. It is important that these diapers should achieve conformability to a body member. Disposable diapers generally are provided with a liquid impermeable backing film, an absorbent layer superposed on the backing film and a liquid permeable topsheet. Diapers are normally fitted to the wearer from a flat state as a result of which they are not completely effective since gaps may develop in the area around the legs through which fluid leaks. In order to overcome this disadvantage, many diapers are now provided with elastic leg stretch components. These stretch components normally comprise elastic bands which are applied to the backing film of the diaper using a hot melt adhesive. The elastic bands are normally applied to the film under stretch and as soon as the hot melt adhesive cools and solidifies, the elastic band relaxes to the original shape, thus pulling the film with it and corrugating the film. This method is expensive and requires a great deal of care to obtain an efficient and proper stretch. Other prior art attempts to overcome the problem of leakage include providing an absorbent layer with an hourglass-like shape or sealing an elastic band between the backing film and the topsheet along the longitudinal edge while in stretch condition for some conformance around the legs. The former approach is accompanied by a reduction in the amount of absorbent material in a critical area and further does not completely avoid gap formation. The latter approach, although decreasing gap formation, has tended to produce a less comfortable product especially if the wearer is an infant. The sealing of an elastic band to the topsheet and backing film may be carried out by the application of adhesive to the band or to both backing film and topsheet. This method of anchoring the rubber band is a cumbersome procedure and moreover tends to produce a harsh feeling on the surface contacting the wearer's skin.
Applicant's copending application Ser. No. 286,441 filed July 24, 1981 overcomes the latter disadvantage in that it consists of applying an elastic pressure-sensitive adhesive tape on the outside of the backing film so that there is no adverse feeling on the surface contacting the wearer's skin.
Prior art disposable diapers have also suffered from the disadvantage of being somewhat unyielding and paper-like and incapable of stretching to any extent, i.e., they lacked elasticity and conformability to the body members to which they are applied. U.S. Pat. No. 4,166,464 overcomes the problem of conformability to the body members, by disclosing a diaper having a thin flexible elastic and easily stretchable thermoplastic backing film as well as a liquid permeable topsheet which is extensible or stretchable such as certain nonwoven fabrics. However, even though the backing film is elastic, that portion of the edge of the backing film adapted to be wrapped around a body member does not necessarily conform completely to the shape of the body member so that a certain amount of leakage of fluid may still occur. This problem is overcome in accordance with the present invention, by providing an elastic backing film in which at least one edge of the backing film is so treated so as to provide a shorter elastic side on the diaper, acting as though it contains a separate elastic band. Thus, in accordance with the present invention there is provided a less cumbersome and a less expensive manner of preparing a "stretch" diaper.